In a next generation 5G system, a wireless sensor network (WSN), which intermittently transmits a small packet by targeting massive connection/low cost/low power services, massive machine type communication (MTC), etc. are considered. In case of massive MTC service, connection density requirement is very restrictive, whereas data rate and end-to-end (E2E) latency requirement are very free (for example, connection density: up to 200,000/km2, E2E latency: seconds to hours, DUUL data rate: typically 1-100 kbps).
Generally, connection density is determined by the number of UEs that may be supported. However, since a configuration scheme of reference symbols should maintain low cross correlation between sequences, the number of sequences that may be supported at the same time is restrictive. For example, in case of legacy LTE uplink system, demodulation reference signal (DMRS) may include 17 group hopping patterns and 30 sequence shift patterns. Therefore, to support massive connectivity, a reference signal hopping scheme for more connection density support is required. However, a UE grouping scheme and a reference signal hopping scheme of a non-orthogonal multiple access system for massive connectivity support of a next generation 5G system have not been suggested up to now.